The feeding-stimulatory effects on the yellowtail Seriola quinqueradiata of extracts of the jack mackerel Trachurus japonicus white muscle were studied. Ultrafiltrates of water extracts of the muscle (M.W.cut off 10,000) were charged on a DEAE-Sephadex A-25 at pH 5.5 or CM-Sephadex C-25 at pH 6.5. Effluents and eluates with 0.6M NaCl were freeze-dried and the components were applied in starch pellets to yellowtails, 23-31g in body weight. Their feeding-stimulatory effectiveness was evaluated by counting the number of pellets eaten within the first minute after application.Their stimulatory effects on the gustatory and olfactory receptors of the yellowtail, 230-746g in b.w., were also studied by recording the electrical responses from the palatine taste nerve and olfactory bulb.(1) Feeding-stimulatory effectiveness of fractioned components (a) Components of the effluent through DEAE-Sephadex column were ineffective, while those of the eluate with NaCl were slightly less effective than t
… Morehe untreated extract. (b) Stepwise elution with 0.2M and 0.6M NaCl on the DEAE-Sephadex column yielded two less effective clusters of different components : 0.2M NaCl-eluate contained lactic acid and minhydrin positive compounds, and 0.6M NaCl-eluate inosinic acid. (c) Components of the eluate from CM-Sephadex C-25 were ineffective, while those of the effluent were nearly as effective as the total extract.(2) Gustatory and olfactory neural responses to fractioned components (a) Both gustatory and olfactory systems responded more or less to all fractions tested. (b) The threshold for the total extract was lower in olfactory system than in gustatory system by some three orders. That for some fractions was also so to different degrees while that for others was similar to each other between the two systems. (c) The threshold for both of lactic acid and inosinic acid, present in 0.2M and 0.6M NaCl-eluates from DEAE-Sephadex culumn respectively and considered one of important components, was lower in gustatory system. Less